As power presses have continued to increase in size and capability, the dies for use in such presses have accordingly increased both in size and weight. Much time and energy, hence cost, must be expended each time these dies are changed. It is, therefore, advantageous to provide moving and sliding bolsters or mechanically and electrically controlled carriers to facilitate quick die changes.
In the past, bolsters having sets of wheels driven by hydraulic motors have been extensively used in various applications to carry heavy dies. One such bolster has a set of wheels, a first motor for moving the bolster in and out of the press, and a second motor for raising and lowering the wheels to set the bolster down on the press bed. Another die-changing apparatus utilizes fixed, but vertically adjustable, support legs mechanized by hydraulic motors to lift and move the dies in and out of the press. In still another apparatus, a complicated pneumatic drive system is used for a wheeled, self-propelled bolster; in this system, two sets of four wheels are independently propelled by two pneumatic drive motors communicating with each other by a set of pilot-operated valves to provide the necessary transportation and support of a die assembly into and out of a press.
While these known die carriers are generally suited for their intended purposes, they are complicated in design due to long interconnecting shafts, couplings and clamping mechanisms and require highly skilled operating personnel and the exercise of great care to guard against operating errors and accidents.